In the above Algorithm REF , the core ideas are \(SS^{T} \approx AA^{T}\)  and \(W^{T}W \approx S^{T}S\) . The following lemma gives a proof for \(W^{T}W \approx S^{T}S\)  in [1]}, then we generalize the proof from \(W^{T}W \approx S^{T}S\)  to \(SS^{T} \approx AA^{T}\) .
